Currently, with a further study and development of laser techniques, lasers are applied more and more widely as their performances are further improved and their costs are gradually reduced. However, during the application of laser pulses, since the irradiation duration is very short, it is necessary to perform multiple overlapped irradiations with laser pulses. Meanwhile, with respect to operations less demanding on energy, it may be necessary to filter out part of the energy, which results in waste of the energy.
For example, in active-matrix organic light emitting diode (AMOLED) display screen techniques, low temperature polysilicon thin film transistors having higher carrier mobility are generally used for driving. An approach of laser annealing is often adopted for the manufacture of polysilicon. In other words, when an amorphous silicon thin film is irradiated by an excimer laser, the amorphous silicon will be molten after laser irradiation and re-crystallized into polysilicon. Taking laser pulses of 500 KHz as an example, each pulse occupies 28 ns, leaving the rest 1972 ns empty. Since grains obtained during the irradiation duration (28 ns) have a very small size, overlapped irradiation is required in order to obtain a larger grain size. At the same time, energy of a laser light is usually far higher than energy required for melting the amorphous silicon, so it is necessary to filter out part of the laser energy by means of an attenuation device. Therefore, there is a technical need for solving the following problems in the prior art: how to prolong the irradiation duration of laser pulses as much as possible without changing internal structure of the laser; as well as how to re-utilize redundant laser energy for operations less demanding on energy so as to improve the utilization for operating energy of the laser light.